But it required a public-private partnership for the complex 126 kilometre section tunnelling through Toowoomba Ranges to Acacia Ridge in Brisbane's west. The final stretch from Acacia Ridge to Brisbane would have cost another $2.5 billion but was left off the table, possibly to keep the cost of the project down.

Port of Brisbane chief executive Roy Cummins said the Melbourne to Brisbane inland rail project would only be a true freight connection if it went all the way through to the port, saying the "missing link" section should also go to market as a PPP to gauge private sector interest.

"Inland Rail proposes the movement of double-stacked containers, as well as increased volumes of resource and agriculture products. If that is the objective, then a dedicated connection to the Port of Brisbane is imperative," Mr Cummins said.

"We are willing to work with all stakeholders and all levels of government to get it done. Inland Rail without a port connection will be less appealing to any PPP case, but with it a PPP would be a more attractive proposition to market."

The dedicated freight line to the Port of Brisbane has been assessed as a separate project by Infrastructure Australia, but said more planning was needed. It recommended a staged investment of $54 million by 2023 would help the existing route to meet demand until 2040-41, saying there should be action to keep the preserved land corridor.

But Infrastructure Association of Queensland chief executive Steve Abson said it made sense for state and federal governments to sort out the preferred route sooner rather than later and to buy up the land corridor to avoid it being "built out".

He said they should bring the project forward by using an availability PPP, thus making the project more affordable to the Commonwealth and the ARTC in the short term. It would also help with a possible future sale of the inland rail project

"The government is wearing the initial risk in the greenfield stages of the project before the revenue model is proven. But if the port connection is completed, this would future proof the project and ultimately increase the attractiveness of the whole project to the private sector in a future sales process," Mr Abson said.

The Queensland Palaszczuk government has been more focused in recent months in extracting money from the Turnbull government for its $5 billion Cross River Rail project which it says is its number one infrastructure project. It has only allocated $800 million of state funds to the project, expecting the Commonwealth to pick up the shortfall.

The state Labor government was angry no money had been allocated in the recent federal budget, with Prime Minister Malcolm Turnbull saying the state's business case was not up to scratch, with some reports saying the federal government wanted more money to be raised from value capture along the rail route from Brisbane's south to the CBD.